In various optical apparatuses, screens and displaying apparatuses such as liquid crystal displays, used are optical members such as light diffusing films and microlenses, in which fine convexes and concaves are provided on surfaces in order to control projection directions of transmitted light or reflected light. As such optical members, not those simply having random convexes and concaves, but those having concaves and convexes of which shapes, intervals and so forth are highly precisely defined in order to control light paths have been proposed (Patent document 1).
Generally employed as techniques for providing convexes and concaves on surfaces of materials are chemical matting in which a matting agent is mixed in a layer forming a surface, embossing, impressing and so forth. However, in the chemical matting, the matting agent itself has particle size distribution, and in addition, dispersion state thereof is not also completely uniform. Therefore, surface profiles having regularity or highly precisely defined surface profiles cannot be formed. Further, in the cases of embossing and impressing, although production of molds may be difficult depending on shapes of convexes and concaves, they have an advantage that if a mold is once produced, surface convexes and concaves can be easily formed thereafter. However, the same surface convexes and concaves cannot necessarily be formed even with the same mold depending on properties of materials, pressures at the time of pressing and so forth, and it is difficult to form convexes and concaves with good reproducibility on any materials.
There are also proposed methods of producing light diffusing plates or microlenses utilizing photolithography, which is a common technique in the manufacture of semiconductor devices and so forth (Patent documents 2 and 3). In the technique disclosed in Patent document 3, a gray scale mask pattern is used to control thickness of photosensitive film to be solubilized by light exposure, and thereby produce microlenses having convexes of desired shapes. The gray scale mask is a mask in which light transmission distribution is formed by providing a pattern of tones, and a gray scale mask of which light transmission is controlled by changing size or numbers of apertures provided in the mask film is disclosed in Patent document 3.    Patent document 1: International Patent Publication WO2004/021052    Patent document 2: Japanese Patent Unexamined Publication (KOKAI) No. 2004-294745    Patent document 3: Japanese Patent Unexamined Publication (KOKAI) No. 2004-310077